Lay, Col.
Please tell us the cause of earthquakes. Are they due to internal convulsions of the earth or to atmospheric disturbances?
Jacob Sloneker.
Answer.—According to that eminent physicist, F. W. Rudler (see his contribution to the Encyclopedia Britannica on “Earthquakes”), “even at the present day, after all that has been written on the subject, but little is known as to the origin of earthquakes.” The general opinion of investigators is that these agitations proceed from within outward, and are not of atmospheric or other external origin. True, Professor Alexis Perry, of Dijon, France, thought he had discovered relations between the ages of the moon and these recurrences, which seemed to sustain the theory of Zantedeschi, that the liquid nucleus of the earth responds to the moon’s attraction in tides, somewhat as the ocean does: but the theory that the earth has a liquid nucleus covered with only a thin, solid crust, is losing adherents continually. The theory of vibration communicated by meteoric impact has been advanced as accounting for some earthquakes. Another theory is that earthquakes are caused in some instances by steam from water rushing into the bowels of volcanoes, or from explosions of pent-up gases, generated by chemical decomposition of minerals. Others believe that many of these phenomena are due to magnetic disturbances, following eruptions in the sun. The prevailing opinion still is that whatever their origin, whether of one cause, or various causes, the vibrations of every earthquake can be traced to a focus within the earth, and that this lies directly beneath the point of greatest disturbance on the earth’s surface. After the great shock at Naples in 1857, Mr. Mallet, aided by the Royal Society, by determining the wave paths of the shock at twenty-six different stations, was able to locate the focal depth of the earthquake at about five and a half miles; and Dr. Oldham, by observations on the wave effects of the earthquake which occurred at Cachar, India, on Jan. 10, 1869, found that the focus of disturbance must have been about thirty miles below the surface. This is very near the maximum depth at which any earthquake is likely to originate, if we accept the reasoning of that most eminent of all investigators of this class of phenomena, Mr. Mallet, of Dublin, Ireland. There are credible records of between 6,000 and 7,000 earthquakes between 1606 B. C. and 1842 A. D. Professor Fuch’s more careful observations of recent years show that there were probably many times that number of unrecorded ones, since he registered ninety-seven during the year 1875 and 104 during 1876. In view of this fact this subject appears to be one of the most interesting problems of nature and is attracting growing attention, which, it is hoped, will presently lead to definite, satisfactory conclusions.
SOUTHEASTERN DAKOTA.
Plankington, D. T.
Having seen questions in The Inter Ocean inquiring about Dakota, and seeing no answers from this county, I concluded to write and tell what I know of it. Aurora is the fourth county from the eastern boundary and the third from the southern. It is considered by all who have traveled over it as one of the finest in Southern Dakota. The county is forty-eight miles long and twenty-four miles wide. In the northwestern portion are situated the “Wessington Hills.” These extend from northeast to southwest as far as the Missouri. Among them are beautiful broad valleys and lakes of clear water. The climate is all that can be desired. Last summer the days were warm and the nights invariably cool, so that after a hard day’s work you could lie down and rest sweetly. The past winter here, as in all other parts of the Northern States, has been very cold and stormy. One month, however, would take in all of the very cold weather. One foot would cover all the snow that we have had this winter. The soil is a black loam, varying in depth from one to six feet. The shallowest we have found on our land is eighteen inches, and the deepest four feet. It is very productive. Last year the crops yielded as follows: Corn from 25 to 60 bushels per acre, wheat from 20 to 40 bushels, oats from 50 to 80 bushels, barley from 30 to 60 bushels, rye from 40 to 60 bushels, flax from 7 to 22 bushels, buckwheat from 10 to 30 bushels, potatoes from 100 to 300 bushels, and all other vegetables yielded enormously. The way this county is filling up is wonderful. One year ago last fall there were only about 150 people in the county, and to-day there are between 450 and 500, and scores more coming on every train. If emigrants continue coming as they have done for the last eighteen months, this county will soon be filled up. Spring has already opened out with us, and farmers are putting in their wheat and barley. Plankington, our county seat, which hardly had a name eighteen months ago, is to-day a fine little village of over 700 inhabitants. With early and deep planting this country will grow almost anything.
Thomas Jacka.